1) Field of the Invention
The present invention relates to a disk rotary driving apparatus for an optical disk reproducing apparatus or the like and, more particularly, to a disk rotary driving apparatus in an optical disk reproducing apparatus for a compact disk player or the like, capable of reproducing a plurality of types of disks having different sizes.
2) Description of the Prior Art
In a conventional disk rotary driving apparatus in an optical disk reproducing apparatus of the reproduction-only type, such as a CD-ROM disk player or a compact disk player, the rotation of a spindle motor is phase-controlled on the basis of a phase comparison signal between a clock signal separated from a reproduction signal obtained by an optical pickup and a predetermined reference signal.
In this manner, in a compact disk player, a spindle motor and its driver together constitute a PLL (phase locked loop) circuit, thereby rotationally driving a compact disk with high precision.
Optical disks are provided in various diameter sizes, for example, a compact disk can have one of two diameters: 8 (cm) and 12 (cm).
Therefore, the weight of the object that is rotationally driven as a load on the spindle motor changes depending on whether a compact disk having a diameter of 8 (cm) or 12 (cm) is driven.
Accordingly, in a compact disk player for reproducing signals from either of two types of compact disks each having a diameter of 8 (cm) or 12 (cm), the servo gain of a PLL circuit must be automatically switched in accordance with the type of compact disk to be driven. Therefore, various detecting methods are used to detect the disk size of the loaded compact disk.
In a first detecting method, a photoreflector is arranged at a predetermined position in an optical disk reproducing apparatus. The diameter of a loaded optical disk is determined in accordance with the presence or absence of light reflected by the optical disk. In this manner, the disk size is detected.
In a second method, a photointerruptor, instead of a photoreflector, is arranged at a predetermined position in an optical disk reproducing apparatus. As in the first method, the size of a loaded optical disk is detected in accordance with whether light from the photointerruptor is interrupted by the optical disk.
In a third detecting method, mechanical contacts are arranged at a predetermined position in an optical disk reproducing apparatus. As in the first and second methods, the type of optical disk is detected in accordance with the ON/OFF state of the contacts.
In a fourth detecting method, a reproduction light beam is radiated from an optical pickup in an optical disk reproducing apparatus onto a loaded optical disk. The optical pickup detects the presence or absence of a reflected light beam, thereby detecting the type of the loaded optical disk as in the above methods.
Accordingly, one of the above detecting methods is selected in designing an optical disk player. The servo gain of the PLL circuit of the spindle motor is switched on the basis of the detection result obtained by the selected method.
In the first to third detecting methods, however, a mechanism must be provided exclusively for detecting the disk size of a loaded optical disk. Therefore, such an arrangement for an optical disk reproducing apparatus such as a compact disk player is complicated.
In addition, in order to reproduce signals from an 8-cm size compact disk in a compact disk player capable of accommodating only a 12-cm size compact disk, an adaptor, consisting of a synthetic resin or the like, can be mounted on the outer circumference of the 8-cm disk.
In this case, since an 8-cm size compact disk with an adaptor mounted on its outer circumference is rotationally driven, the spindle motor of the compact disk player must be phase-controlled with a servo gain similar to that used to rotationally drive a 12-cm compact disk.
Since, however, the adaptor is not able to reflect light, the loaded compact disk is detected as an 8-cm compact disk by the above-described first and fourth detecting methods. Therefore, the spindle motor is phase-controlled with a servo gain for driving an 8-cm compact disk, resulting in an insufficient servo gain.
In addition, some compact disks have a transparent outer circumference. In this case, in the first, second, and fourth detecting methods, the presence of an 8-cm compact disk may be erroneously detected although a 12-cm compact disk is loaded.